Turn signal/brake light issue - weird controller box ??

[bmackrell]

Hello All,

So I just bought my Cobra a few days ago and spent the holiday weekend sorting it out. For the most part its in great shape with a few paint chips here and there, a cracked windshield and two gauges not working. It was built around 2000 and is probably a MK 1 or an early MK 2 (see other thread).

I noticed that the left rear tail light blinker/brake light was acting funny. The blinker doesn't work but when you press the brakes it works and then the passenger side dims and blinks faster. At first i thought it was a bad ground so opened up the lens' and tested it. Not a bad ground!

Next I took off the switch from the dash and tested the wires for continuity. The signal seemed to indicate the wire running to left blinker was broken. I ran a jumper from the switch directly to the tail light and everything worked. I thought maybe over the years the wire had shorted somewhere under the car. Was going to try and figure out how to run a new wire. Not Fun!

I started unraveling the wires under the dash and found this odd controller box (see pic)

https://thefactoryfiveforum.com/attachment.php?attachmentid=129024&d=1590511215

After googling the part number it seems to be a trailer tail light control unit. It allows you to send both the turn signal and brake signal down the same wire. I'd never seen this in a car so after poking around I think this is whats bad.

Is this common practice when building a FF kit ,or a weird homemade solution to reduce the number of wires in the wiring harness?

Any help would be appreciated.

Regards,

BillMac

[Big Blocker]

Many builders have used a trailer adapter to make their rear lights work differently than was originally designed into the F5 wiring scheme. Some have had issues with this approach, some not. The earlier models were prone to faulty operation or the builder could never get it to work.

The F5 original idea was to have the upper of the two lens be your brake light, the lower, the turn signal. Many of us wanted a little more indication, especially those of us living in the southwestern states with an over abundance of sunlight . . . I, personally, have both upper AND lower for both brake and turn signal - no trailer adapter.

My best advice to you would be to trace the faulty wire and repair it at the break or fault. Also, how many dash indicators do you have? Builders with only one needed diodes to prevent electrical back-feed, the diode(s) could have gone bad.

That being said, there are alternatives that do not need a trailer adapter to get the same effect. Circuits are available that require relays and some rewiring to accomplish.

Good luck.

Doc

[bmackrell]

Thank you Big Blocker.

I've been researching this since last night and I'm finding all the old threads with you and Jeff K. My buddy who shares the shop with me is a master mechanic and was giving me the stink eye when we pulled out the trailer adapter. :)

There's only one indicator on the dash for blinkers. I'll get behind there this week and see whats up.

Regards,

BillMac